Dual band phased array element

ABSTRACT

A dual band phased array apparatus for exicting in a single microwave waveguide a phased array element with signals having a substantial frequency difference.

United States Patent 11 1 Mailloux 1451 May 6,1975

[ DUAL BAND PHASED ARRAY ELEMENT [76] Inventor: Robert J. Mailloux, 98 Concord Rd., Wayland, Mass. 01778 [22] Filed: May 30, 1974 21 Appl. No.: 474,561

2,961,659 11/1960 Kuecken 343/778 Primary Examiner.lames W. Lawrence Assistant Examiner-Marvin Nussbaum Attorney, Agent, or Firm-William Stephanashen [5 7] ABSTRACT A dual band phased array apparatus for exicting in a single microwave waveguide a phased array element with signals having a substantial frequency difference.

10 Claims, 3 Drawing Figures [56] References Cited UNITED STATES PATENTS 2,943,324 6/1960 Sichak 333/1 X A l0-z DUAL RANT) PHASIED ARRAY ElhliZlVlllEld'll BACKGROUND OF THE INVENTEON The present invention relates broadly to phased array antenna elements and in particular to a dual band phased array antenna element.

in the prior art an array of antennas is an arrangement of several individual antennas so spaced and phased that their individual contributions add in the preferred direction and cancel in other directions. One practical objective is to increase the signalto-noise ratio in the desired direction. Another objective may be to protect the service area of other stations, such as broadcast stations.

The broadside array is a preferred arrangement to provide control over the radiation pattern. In this array, antennas are placed in a line perpendicular to the bidirectional beam. individual antenna currents are identi cal in magnitude and phase. The array can be made undirectional by placing an identical array 90 to the rear and holding its place at 90. The directivity of such a box array increases with the length or aperture of the array individual pairs of antennas in the broadside array must be spaced 217 for maximum gain with two pairs: spacing increases as more pairs are used in the array.

Previous techniques have interlaced array elements of different frequencies so that each of the interlaced arrays occupies only a part of the total aperture. Other prior art techniques have used highly loaded elements with very close spacing for wide band performance, but in such cases simultaneous use of two frequencies is excluded by the single set of terminals and single phase shifter. In addition, many more phase shifters than nec essary are required and used at the lower frequencies because of the unusually close spacings. The use of independent low and high frequency circuits allows simultaneous operation at two frequencies, with good et ficiency because each frequency uses the whole array aperture, and with economical use of phase shifters due to wide spacings.

SUMMARY The present invention provides the means for exciting a phased array element with signals that differ substantially in frequency. The dual band phased array apparatus comprises a single microwave waveguide which is excited by independent input ports. The two circuits occupy the same array aperture with dielectric loading of the waveguide to prevent the signals from interferring with each other. The dual band phased array apparatus provides the means of exciting given aperture to form independently steered beams in different frequency bands.

It is one object of the invention, therefore, to provide an improved dual band phased array apparatus capable of exciting in a single aperture signals that differ substantially in frequency.

it is another object of the invention to provide an improved dual band pahsed array apparatus capable of exciting a single waveguide aperture to form independently steered beams.

It is yet another object of the invention to provide an improved duai band phased array apparatus having a single microwave waveguide which is excited by two independent input parts.

These and other advantages, features and objects of the invention will become more apparent from the following description taken in connection with the illustrative embodiment in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view, partly in section, of the dual band phased array apparatus in accordance with the present invention.

FIG. 2 is an isometric view, partly in section, of the dual band phased array apparatus for X-band and C- band operation, and,

FIG. 3 is a schematic diagram of the dual band phased array element arranged in an array.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. I, there is shown a dual band phased array apparatus 10 for exciting a phased array element with signals that differ substantially in frequency. This is accomplished in the dual band phased array apparatus l0 by designing two circuits into the same microwave waveguide, and by dielectrically loading the waveguides so that the two signals do not interfere. With proper design the higher frequency signal can have the appropriate phase relationships across the final aperture to scan its beam over relatively side angular sectors.

The high frequency circuit comprises four waveguides channels 12, l3, l4, 15 with tapered transitions into dielectrically loaded sections. The waveguides 12-44 are excited by conventional transitions from coaxial lines or by other waveguides with phase shifters. The tapered dielectric slabs 16, 17, 18, 19 are inserted in the waveguide channels 12- 15 to provide dielectric loading. The purpose of the dielectric loading is to confine the fields very close to the dielectric slabs 16l8, and when this is done properly the central I-l-plane divider 20 between two adjacent waveguides may be removed without any substantial coupling of the adjacent Waveguides. This wall divider 20 is removed in the front part of the circuit and a probe 22 for exciting the lower frequency signal is also mounted in the center of the oversize waveguide. This probe 22 does not interfere with the high frequency signals traveling down the guide because they remain confined very closely to the dielectric slabs l6-l8. Some tapering of the slabs is shown near the radiating aperture to improve scan match.

The crucial feature of this high frequency circuit is that the adjacent high frequency signals couple minimally-except at the radiating aperture. Preliminary measurements have achieved coupling levels less than -20dB over the X-band frequency range between 8.5 and 10.5 GHZ, using A inch slabs of dielectric with a dielectric constant @9. These results indicate that the direct coupling of adjacent high frequency signals will be negligible compared to the unavoidable coupling at the radiating aperture.

The low frequency circuit comprises of two waveguides 24, 26 approximately twice the width of each of the high frequency waveguides and approximately the same height as the high frequency waveguides. These waveguides are excited in pairs by means of a dipole probe 22 which is connected to the coaxial line 40. The height of each pair is approximately twice that of the high frequency guide and placed or held together to match with the X-band waveguides. A slot 21 is cut through the common waveguide wall to allow passage of the coaxial line 40. This slot 21 flares out in the vicinity of the dipole 22 so as not to short circuit it. The coaxial line 40 which passes along this slot 21 is held in place by dielectric spacers (not shown), and terminates in the balun fed dipole 22. The balun fed dipoles 22 are state of the art and are well known to those skilled in the art. Other dipole types would function as well in the present invention. The dipole probe 22 is placed a fixed distance, L in front of where the high frequency waveguides join the double width waveguides 24, 26 and the E-plane septum and high frequency waveguides serve as a shorted back-plate for the low frequency probe. The dielectric slabs 16-19 in the half height C-band guides may be tapered somewhat as shown to improve array high frequency radiation properties. The distance, L, is measured from the front face of the four high frequency (X-band) waveguides, and this distance is used to tune the probe for proper impedance match at the low frequency. The low frequency waveguides 24, 26 will operate well below the cutoff of the particular waveguide type, because of the heavy dielectric loading.

Turning now to FIG. 2, there is shown a crosssectional view of the dual band phased array apparatus of FIG. 1. The cross sectional view is taken along line AA of FIG. 1. FIG. 2 shows in greater detail the features for X-band and C-band operation comprising the four X-band waveguides as shown in FIG. 1 with a very thin coaxial line 40A passing through along the axis of the intersection of these guides to feed the C-band dipole (not shown). Adequate space for this coaxial line 40A can be made by removing some of the X-band wall material at the waveguide corners, or by increasing the spacing between the waveguides slightly. The tapered dielectric slabs 3033 have a dielectric constant F9. This dielectric constant may be reduced at the expense of increased cross coupling of the X-band signals within in the C-band waveguide region. The X-band signals enter through the high frequency waveguide inputs as in FIG. 1, and may be excited from coaxial lines, or space feeding techniques. The X-band phase shifters (not shown) located in additional waveguide or coaxial line sections are conventional devices which are well known to those skilled in the art.

In this manner, and depending upon design constraints, the invention operates within two distinct frequency bands. These frequencies may differ by a factor of up to four, or by less than an octave if desirable. In either case, a distinguishing feature of the invention is that it provides two independent sets of terminals for the high and low frequencies.

FIG. 3 shows a plurality of dual band phased array elements arranged in an array. One of the dual band phased array elements 50 has been outlined heavily in black so as to be clearly defined within the array arrangment.

Although the invention has been described with reference to a particular embodiment, it will be understood to those skilled in the art that the invention is capable of a variety of alternative embodiments within the spirit and scope of the appended claims.

It is claimed:

1. A dual band phased array element comprising in combination means for forming a plurality of first waveguide sections, said plurality of first waveguide sections having a central wall divider, said plurality of first waveguide sections being dielectrically loaded,

means for forming a plurality of second waveguide sections, said plurality of second waveguide sections being located within said plurality of first waveguide sections, said plurality of second waveguide sections being located at one end of said plurality of first waveguide sections, and

a low frequency coaxial line contained within said plurality of first waveguide sections and extending into said plurality of second waveguide sections, said low frequency coaxial line supplying the input signal to said plurality of second waveguide sections.

2. A dual band phased array element as described in claim 1 wherein said means for forming said plurality of first waveguide sections comprises four high frequency waveguide sections arranged to form the waveguide unit, each of said four high frequency waveguide sections having one common wall, said four high frequency waveguide sections having a common corner.

3. A dual band phased array element as described in claim 1 wherein dielectric slabs are contained within said plurality of first waveguide sections, said dielectric slabs providing the dielectric loading of said plurality of first waveguide sections.

4. A dual band phased array element as described in claim 2 which further include a slot in said common comer of said plurality of first waveguide sections, said slot extending into the common wall of said plurality of second waveguide sections, said low frequency coaxial line being disposed within said slot, said low frequency coaxial line being insulated from said plurality of first waveguide sections and from said plurality of second waveguide sections.

5. A dual band phased array element as described in claim 1 wherein said low frequency coaxial line has a dipole mounted at one end thereon, said dipole extending into said plurality of second waveguide sections.

6. A dual band phased array element as described in claim 3 wherein said dielectric slabs have a dielectric constant equal to 9.

7. A dual band phased array element as described in claim 3 wherein said dielectric slabs are tapered at both ends.

8. A dual band phased array element as described in claim 5 wherein said dipole operates in the C band.

9. A dual band phased array element as described in claim 5 wherein said dipole is positioned at a predetermined distance from the end of said central wall divider.

10. A dual band phased array element as described in claim 6 wherein plurality of second waveguide sections comprises two low frequency waveguides. 

1. A dual band phased array element comprising in combination means for forming a plurality of first waveguide sections, said plurality of first waveguide sections having a central wall divider, said plurality of first waveguide sections being dielectrically loaded, means for forming a plurality of second waveguide sections, said plurality of second waveguide sections being located within said plurality of first waveguide sections, said plurality of second waveguide sections being located at one end of said plurality of first waveguide sections, and a low frequency coaxial line contained within said plurality of first waveguide sections and extending into said plurality of second waveguide sections, said low frequency coaxial line supplying the input signal to said plurality of second waveguide sections.
 2. A dual band phased array element as described in claim 1 wherein said means for forming said plurality of first waveguide sections comprises four high frequency waveguide sections arranged to form the waveguide unit, each of said four high frequency waveguide sections having one common wall, said four high frequency waveguide sections having a common corner.
 3. A dual band phased array element as described in claim 1 wherein dielectric slabs are contained within said plurality of first waveguide sections, said dielectric slabs providing the dielectric loading of said plurality of first waveguide sections.
 4. A dual band phased array element as described in claim 2 which further include a slot in said common corner of said plurality of first waveguide sectioNs, said slot extending into the common wall of said plurality of second waveguide sections, said low frequency coaxial line being disposed within said slot, said low frequency coaxial line being insulated from said plurality of first waveguide sections and from said plurality of second waveguide sections.
 5. A dual band phased array element as described in claim 1 wherein said low frequency coaxial line has a dipole mounted at one end thereon, said dipole extending into said plurality of second waveguide sections.
 6. A dual band phased array element as described in claim 3 wherein said dielectric slabs have a dielectric constant equal to
 9. 7. A dual band phased array element as described in claim 3 wherein said dielectric slabs are tapered at both ends.
 8. A dual band phased array element as described in claim 5 wherein said dipole operates in the C band.
 9. A dual band phased array element as described in claim 5 wherein said dipole is positioned at a predetermined distance from the end of said central wall divider.
 10. A dual band phased array element as described in claim 6 wherein plurality of second waveguide sections comprises two low frequency waveguides. 